Immobilized Ionic Chloride-Mediated Quasi-Homogeneous Catalysis System for Boosting Selective Conversion of Fructose to 5-Hydroxymethylfurfural

5-Hydroxymethylfurfural (HMF), which is one of the most crucial biomass platform compounds, is typically obtained from fructose by dehydration. However, solid-acid-catalyzed dehydration suffers from low HMF yields, while homogeneous chloride promoters induce separation challenges. Herein, we employed commercial ionic chloride-form resin beads (DP-Cl) as a heterogeneous chloride promoter, synergistically with acidic resin Amberlyst-15 (A-15), to efficiently catalyze fructose dehydration to HMF. Under optimized conditions, 91% of HMF selectivity with a yield of 73 mol % was obtained, and A-15/DP-Cl remain stable over 8 consecutive cycles. Adsorption experiments, 1H nuclear magnetic resonance spectroscopy, attenuated total reflection Fourier-transform infrared, and kinetic studies revealed that Cl– facilitates the formation, adsorption, and dehydration of β-d-furanose (β-f), thereby lowering the reaction energy barrier. This work establishes a quasi-homogeneous catalytic system that integrates the high activity of homogeneous catalysis with the easy recovery of heterogeneous catalysts, providing a practical approach for high-value biomass utilization.